1. Field of Invention
The present invention relates to a fluorescent lamp, and more particularly to a high performance fluorescent lamp which has low manufacturing cost and simple structural configuration for manufacture.
2. Description of Related Arts
The fluorescent lamp is basically a low pressure mercury discharge lamp. A conventional fluorescent generally comprises an air-tight tubular casing coated with fluorescent powder or phosphors powder at an inner wall thereof and filled with lower pressure mercury vapor and inert gases, and two electrodes at two ends of the tubular casing. When the electrodes are connected to a power source and electrified, the voltage between the two electrodes will break down the inert gases and the electron can go through between the electrodes. The mercury atoms are excited by the electrons for emitting Ultraviolet (UV) light. Then, the coating of fluorescent powder or phosphors powder will convert the UV light to visible light. Accordingly, the performance of the fluorescent lamp is controlled by the mercury vapor pressure, inert gases, and the phosphor powder coating.
In the traditional fluorescent lamp, pure mercury is filled into the tubular casing of the lamp. When the lamp operates at 25° ambient temperature, the lamp has the highest light output. The mercury vapor pressure is able 0.8 Pa. When the ambient temperature increased, the mercury vapor pressure is correspondingly increased and the self-absorption in the vapor reduces the yield of UV and visible light. Therefore, when the mercury vapor pressure is increased, the light output will be reduced. In order to improve the operation temperature of the fluorescent lamp, the mercury vapor pressure should be regulated. A common way to regulate the mercury vapor pressure is using amalgam. Accordingly, amalgam is mercury mixed with various alloys, wherein different mixtures of the amalgam will have different operation temperature ranges. Amalgam, to be used in the lamp for higher operation temperature is expensive and needed an auxiliary amalgam. A fluorescent lamp with low temperature amalgam can operate at 35° C. ambient temperature.
U.S. Pat. No. 4,972,118 disclosed an improved fluorescent lamp with amalgam adapted to be operated at 45° C. to 55° C. ambient temperature, wherein the amalgam has a main amalgam and an auxiliary amalgam. The main amalgam is located in a special container. An expensive high temperature amalgam has to be used if the lamp needs to be operated at higher ambient temperature. Therefore, such lamp is extremely expensive and is difficult to manufacture.
The nature light source on earth is sunlight. Sunlight is considered as natural light to be comfortably visible to the human eye normally. Human being can see different colors based on wavelength of sunlight within the visible spectrum. The range of wavelengths that human being can perceive is known as visible light. In other words, to generate a light similar to sunlight spectrum is an “ideal light”. Sunlight spectrum is from UV light to IR (infrared) light. However, human being can only see portion of sunlight. According to CIE chromaticity or color space, the wavelength of light that human eye can see is from 380 nm to 700 nm. Therefore, the spectrum of the “ideal light” should be from 380 nm to 700 nm.
All fluorescent lamps use fluorescent powder or phosphors powder to convert ultraviolet light to visible light. U.S. Pat. No. 4,199,707 disclosed a basic light spectrum of the fluorescent lamp, wherein in the light spectrum, there is almost no light wavelength from 380 nm to 420 nm.
According to Ohm's Law, V=R*I, it states that doubling the voltage will double the current. It is called “Positive Voltage-Current Characteristic”. The incandescent lamp has the “Positive Voltage-Current Characteristic”. For fluorescent lamp, the lamp impedance R is not a constant number. The lamp impedance R will be increased when the lamp current is reduced. It is called “Negative Voltage-Current Characteristic”. It means that doubling the current will cause less doubled the voltage. It will generate more heat and lower the efficiency of the lamp.